1. Field of the Invention
The present invention relates to a method and apparatus for improving the detection of trace amounts of total sulfur in fluids such as fuels and petroleum distillates using UV fluorescence.
More particularly, the present invention relates to a method and apparatus for improving the detection of trace amounts of total sulfur in fluids such as fuels and petroleum distillates using UV fluorescence, where the method and apparatus involve removing and/or chemically deactivating interfering nitrogen species prior to UV fluorescence detection of sulfur.
2. Description of the Related Art
For the most part, detection of sulfur by UV fluorescence is normally considered to be relatively free of any significant interference from complete oxidation of most hydrocarbon samples and combustion byproducts. However, it has been noted that when analyzing iso-octane blanks or low-level sulfur samples, higher than expected sulfur readings are routinely encountered with UV fluorescence methods when compared to data acquired from other equally effective analytical methods such as lead-acetate tape instrumentation. There have been numerous theories behind this discrepancy, but until now, a satisfactorily credible explanation has remained elusive.
Although the UV fluorescent instruments include calibration software routines that can subtract “blank counts” or constant values from analyzed samples, frequently such offsetting changes whenever a combustion tube or gas supply bottle is changed. Recently, exceptionally high “background” counts relative to what would be expected have been noted. Moreover, it has also been noted that water samples create “no background,” while alcohols show increased “background” counts as the molecular weight of the alcohol increases.
Thus, there is a need in the art for an improved UV fluorescent apparatus and associated method for trace sulfur detection that is substantially free of a hereto unknown source of interference.